When is the best time of day for Christina to study? in the morning, instead of going to swim practice
in the late afternoon, instead of relaxing
in the early evening, during dinner
in the late evening, before bed

Usually after school time. but is there any backstory on christina? what does her day look like?

It is useful for historians to write narratives so that history can be passed on from their point of view.  think about a story being told in third person, then think about it again being told in first person, by someone who actually experienced the event.